Introduction. This study describes the identification and partial characterization of persistence-inducing factors (PIFs) from staphylococci.
Hypothesis/Gap Statement. Increases in persisters during mid-log phase growth indicate that quorum-sensing factors might be produced by staphylococci.
Aim. To identify and partially characterize PIFs from
Staphylococcus epidermidis
RP62A and
Staphylococcus aureus
SH1000.
Methodology. Others have demonstrated a significant increase in persister numbers during mid-log phase. Inducers of this mid-log increase have yet to be identified in staphylococci. Optical density at 600 nm (OD600) was used instead of time to determine when persister numbers increased during logarithmic growth. Concentrated culture filtrates (CCFs) from
S. epidermidis
and
S. aureus
were obtained at various OD600s and following incubation at 16 h. The CCFs were used to develop a PIF assay. The PIF assay was used to partially characterize PIF from
S. epidermidis
and
S. aureus
for sizing of PIF activity, temperature and protease sensitivity and inter-species communications.
Results. The optimal OD600s for
S. epidermidis
and
S. aureus
PIF assays were 2.0 and 0.5, respectively. The highest PIF activity for both species was from CCF following incubation overnight (16 h).
S. epidermidis
’ PIF activity was decreased by storage at 4 oC but not at 20 oC (16 h), 37 oC (1 h) or 100 oC (15 min).
S. aureus
’ PIF activity was decreased following storage at 4 oC (2 weeks) and after boiling at 100 oC for 5 min but not after incubation at 37 oC (1 h). PIF activity from both species went through a 3000 molecular weight cutoff ultrafilter. Proteinase K treatment of
S. aureus
PIF decreased activity but did not decrease the PIF activity of
S. epidermidis
. PIF from
S. epidermidis
did not increase persisters when used to treat
S. aureus
cells and nor did PIF from
S. aureus
increase persisters when used to treat
S. epidermidis
cells.
Conclusions. Attempts to discover PIFs for staphylococci were unsuccessful due to the time-based means used to identify mid-log. Both staphylococcal species produce extracellular, low-molecular-weight inducers of persistence when assayed using an OD600 -based PIF assay.
Purification and Partial Characterization of an Acidic α-Glucan–Protein Complex from the Fruiting Body ofPleurotus sajor-cajuand Its Effect on Macrophage Activation